The present invention relates to a diketo pyrrolo pyrrole pigment, in particular to a novel form of a 1,4-diketo-3,6-di(4-tertiary butyl phenyl)pyrrolo[3,4-c]pyrrole pigment having distinguished color characteristics and x-ray diffraction pattern, a method for its preparation and the use of the pigment in high molecular weight organic materials.
Diketo pyrrolo pyrrole pigments are well known for their bluish red to orange shades with high pigment performance, such as excellent weatherability and outstanding heat stability.
1,4-diketo-3,6-di(4xe2x80x2-tertiary butyl phenyl)-2,5-dihydro pyrrolo [3,4-c]pyrrole pigment of the formula I: 
was first described in U.S. Pat. No. 4,415,685 as a reddish orange pigment. U.S. Pat. No. 4,579,949 discloses a method for its preparation and describes the resulting pigment as red.
A commercially available 1,4-diketo-3,6-di(4xe2x80x2-tertiary butyl phenyl)-2,5-dihydro pyrrolo[3,4-c]pyrrole pigment is the IRGAZIN DPP Orange RA with the Color Index designation of C.I. Pigment Orange 73. This product shows a bright reddish orange shade and manifests a high pigment performance.
In comparison to the commercially available 1,4-diketo-3,6-di(4xe2x80x2-tertiary butyl phenyl)-2,5-dihydro pyrrolo[3,4-c]pyrrole pigment, the new diketo pyrrolo pyrrole pigment form shows a considerably higher chroma, a greater opacity, a yellower hue, and a different X-ray diffraction pattern.
U.S. Pat. No. 2,857,400 and U.S. Pat. No. 5,194,088, which are each incorporated herein by reference, describe finishing methods of organic pigments by premilling and after treatment in polar solvents. These patents describe the ripening of the pigment particles but do not reveal a crystal phase conversion of a diketo pyrrolo pyrrole pigment.
An organic pigment having a higher chroma is more valuable because it is more attractive and offers more styling opportunities in combination with other pigments. Thus, a difference in chroma is generally of considerable commercial importance. Due to the outstanding fastness properties, its excellent Theological properties and unique color characteristics, the pigment described herein is highly suited for use in plastics and coatings applications, particularly in automotive coating systems.
The present invention relates to a 1,4-diketo-3,6-di(4xe2x80x2-tertiary butyl phenyl)-2,5-dihydro pyrrolo[3,4-c]pyrrole pigment in its alpha-II form. The pigment is characterized by its C.I.E color space values in masstone of L=55-60, C=73-80, h=44-50 measured from a panel coated to complete hide with a basecoat/clearcoat paint system. More preferably, the C.I.E color space values in masstone are L=55.5-60, C=73.5-80, h=44.5-50, most preferably L=56.5-60, C=75.5-80, h=45-50.
At least 50 percent of the primary pigment particles have a particle size in the range from 0.1 to 0.5 micrometers as determined by electron micrograph. The pigment has a specific surface area of about 15xc2x18 m2/g as determined by the BET method.
The inventive pigment can be further characterized by an x-ray diffraction pattern that exhibits two strong peaks corresponding to xc2x10.2 two xcex8 double glancing angles of 5.6 and 23.2, two medium strength peaks corresponding to 16.1 and 27.2, and eight relatively weak peaks corresponding to 12.3, 12.9, 15.4, 17.0, 17.4, 17.9, 20.9 and 24.6.
The present invention further relates to a process for the preparation of said 1,4-diketo-3,6-di(4xe2x80x2-tertiary butyl phenyl)-2,5-dihydro pyrrolo[3,4-c]pyrrole pigment. The process includes the steps of premilling an alpha-I form of a 1,4-diketo-3,6-di(4xe2x80x2-tertiary butyl phenyl)-2,5-dihydro pyrrolo[3,4-c]pyrrole pigment, followed by a conversion into the alpha-II form by an after treatment in an organic solvent, optionally in the presence of a diketo pyrrolo pyrrole- or 6,13-dihydroquinacridone derivative as a crystal size and crystal phase director. Preferably, the alpha-I form of the 1,4-diketo-3,6-di(4xe2x80x2-tertiary butyl phenyl)-2,5-dihydro pyrrolo[3,4-c]pyrrole pigment is obtained by reacting a succinate with a nitrile in an organic solvent and in the presence of a strong base at an elevated temperature.
The present invention further relates to a composition comprising a high molecular weight organic material and an effective pigmenting amount of the alpha-II form of the 1,4-diketo-3,6-di(4xe2x80x2-tertiary butyl phenyl)-2,5-dihydro pyrrolo[3,4-c]pyrrole pigment. The high molecular weight organic material is preferably selected from the group consisting of cellulose ethers, cellulose esters, polyurethanes, polyesters, polycarbonates, polyolefins, polystyrene, polysulfones, polyamides, polycycloamides, polyimides, polyethers, polyether ketones, polyvinyl halides, polytetrafluoroethylene, acrylic and methacrylic polymers, rubber, silicone polymers, phenol/formaldehyde resins, melamine, formaldehyde resins, urea/formaldehyde resins, epoxy resins and diene rubbers or copolymers thereof and mixtures thereof. The high molecular weight organic material can be an industrial or automotive paint or ink coating.
The present invention further relates to a process for coloring a high molecular weight organic material by incorporating an effective pigmenting amount of the inventive pigment into the high molecular weight organic material.
The present invention also relates to an article of manufacture made from the composition described above, wherein the composition is calendered, cast, molded into shaped articles or processed into fibers.